Improving the views integration of the entity share client module

Problem/Motivation

The entity share client module provides an EntityImportStatus entity to track the various details of data entities that have been imported to your site. In its current implementation, It is possible to create a view of these EIS entities but it is not possible to join in the actual entity data tables to the view in order to display the field data of those imported entities. Likewise, it is possible to have views of data entities but there is no way to join in the EntityImportStatus data into those views (for example, if you wanted to do something like edit the default admin/content page to display which site the imported data entities came from).

Proposed resolution

1. Override the views_data handler on the EntityImportStatus entity type to also support adding views relationships to join in the fields from all data entity tables.
2. Implement hook_views_data_alter to add views relationships to each existing data entity type to allow joining in the related EntityImportStatus fields.